Hypodermic needles have been used to introduce therapeutic medications to the body for over a century. Needles of a similar construction, that is, a tubular metallic cannula with a lumen running the axis of the needle is sharpened and attached to a syringe, are also used to extract blood and other fluid from the body. The use of these needles for these purposes has long been the method of last resort, especially for the injection of medications because of the pain associated with the forcing of the needle into the body. Over the years manufacturers of these hypodermic needles have learned that the smaller the diameter of the needle and the sharper the point of the needle, the more comfortable the injection would be. Today, it is common to inject medications with very fine needles such as those made by the Becton Dickinson Company of New Jersey.
However, there is a limit to the degree to which the diameter of these needles may be reduced. One limitation is established by the flow rate of the liquid along the cannula which is related to the fourth power of the diameter of the needle. As the diameter is reduced, the flow rate rapidly decreases. If a certain volume of fluid is to be injected and the diameter to be reduced, either the pressure used to move the fluid along the cannula or the time allotted for introducing the fluid will increase. Fluids such as insulin for the treatment of diabetes are usually injected in the home by the person with diabetes. Such individuals are unable to exert sufficient pressure to inject their insulin in a satisfactorily short period of time if the fineness of the needle, expressed in gauge, is finer than 31 G. At 31 G fineness, the injection, while being considerably more comfortable than 28 G and 29 G needles used in earlier years, is still sufficiently uncomfortable to be the number one reason why persons with diabetes strongly prefer to not be on insulin if at all possible. Other medical uses of hypodermic needles are also known to be painful. These uses include venipuncture for drawing blood, dialysis, and
One way to increase the flow rate of a fluid passing through a cannula is to place openings along the side of the needle. Such needles, known as sprinkler needles are known in the art and are described, for example, by Gross in U.S. Pat. No. 6,261,272, incorporated herein in its entirely be reference. The additional openings on the side of the needle provide additional access to the tissue creating both a shorter path to the tissue, thereby reducing the distance the fluid has to travel and increasing the area of the access to the tissue thereby increasing the effective area of the outlet of the needle. These advantages exist both in the delivery of the fluid to the tissue and the extraction of fluid from the tissue. Sprinkler needles have the additional advantage of delivering the fluid to a larger volume of tissue thereby reducing the pressure needed to deliver the fluid and increasing the surface area of tissue exposed to the fluid thereby enhancing the absorption rate of the fluid by the body.
While sprinkler needles have a performance advantage over straight cannula needles, this performance advantage comes at a significantly higher manufacturing cost. The additional openings must be cut in the sides of the needle which takes more time and additional manufacturing setups, and these openings must further be deburred to make sure the pain of insertion is low. Hence there exists a need for improved hypodermic needles.